Circuit arrangement in television receivers



@c&. 8, 3949. ANDRiEU 2,257,396

CIRCUIT ARRANGEMENT IN TELEVISION RECEIVERS Filed Feb. 15, 1937 llllllIII. a

INVENTOR ROBERT ANDRIEU BY m gww ATTORNEY Patented Oct. 8, 1940 UNITEDSTATES ATET FFICE CIRCUIT ARRANGEDIENT IN TELEVISION RECEIVERS tion ofGermany Application February 15, 1937,-Serial No. 125,715 In GermanyFebruary 20, 1936 6 Claims.

The invention concerns a circuit arrangement for control of saw-toothgenerators in television receivers. It is here assumed that thegenerators require a negative potential impulse at their input tube forthe production of the short arm of the saw-tooth curve and further thatthe detector circuit is connected in series in the manner that duringthe synchronizing impulse a negative potential exists with respect tocathode at control grid of input tube.

In accordance with the invention the detector circuit is in this casedirectly connected with the control grid of input tube through aresistance.

The invention may be used in principle for all conditions sufficingabove assumptions.

Two embodiments of invention will be explained in what follows with theaid of the draw- In Figure 1 is represented the course of the lowfrequency for the case that a carrier wave of a certain finite value Sis increased by image currents and decreased by synchronizing impulsesbelow this value S down to zero. Value S may thereby correspond to theblack image points so that the image points of maximum brightness arealso reproduced by a carrier wave amplitude of maximum size. But, on theother hand, to value S may also be coordinated the image points ofmaximum brightness, in which case the maximum carrier wave amplitudescorrespond accordingly to the black image points. The range of thecarrier wave amplitude below size S is in both cases reserved for signalindication alone, for instance, by the synchronizing impulses.

A circuit arrangement suitable for a transmitting method according toFig. 1 is illustrated in Fig. 2.

an designates the secondary of a transformer whose primary is joined tothe high frequency amplifier. The detector circuit consists of thissecondary winding, a rectifier H, as well as a resistance 12 withcondenser connected in parallel thereto and it is grounded over apotential source l3. Point P of detector circuit is connected through aresistance M with the control grid of input tube E5 of a saw-toothgenerator. The cathode of tube I 5 is grounded.

The circuit arrangement according to Fig. 2 operates in the manner thatthere appears a potential for values of the carrier wave amplitude andtherewith for values of the potential appearing at resistance l2 belowvalue S at point P, said potential being below that of the earthpotential. The size of potential source I3 is dimensioned in the mannerthat with that potential drop at resistance l2 which corresponds tovalue S, point P is just impressed with earth potential. As a resultthereof the synchronizing impulses which as understood produce accordingto Fig. 1 the potential drop zero at resistance I2, cause the ap- 5pearance at the control grid of tube I5 of a negative potential withrespect to cathode. But carrier wave amplitudes and therewith alsoamounts of the potential drop at resistance 2 which exceed value S raisepoint P to a positive potential with 10' respect to earth, but, on theother hand, there is produced by the grid current generated by positivepotentials in point P a potential drop at resistance I4 with the resultthat the control grid potential does not rise through the image cur- 15rents noticeably above value corresponding to value S. The mode ofoperation of saw-tooth generator need not be explained again in this connection, since it is described in application Ser. No. 61,499, filedJan. 30, 1936. 20

Fig. 3 has reference to a transmitting method whereby a carrier waveamplitude is modulated by the image currents from zero to value G, thesynchronizing signals being given by carrier wave amplitudes which aregreater than that corre- 25 sponding to value G.

A receiving arrangement in accordance with invention and suitable forthis method of transmission is shown in Fig. 4..

Therein the symbols It) to I2, I4, l5 and P have 30 the same meaning asin Fig. 2. But the detector circuit is grounded through a direct currentpotential source 56 of reversed polarity of that in Fig. 2 and thetransmitting direction of detector 1 I is reversed with respect to Fig.2. 35

The circuit scheme according to Fig. 4 operates in the manner that earthpotential appears at a point P with a carrier wave amplitude of the sizeG, in other words, that the potential [6 is as large as value G. Hence,the synchronizing 4o signals of Fig. 3 produce at point P a negativepotential with respect to cathode of tube l5. As to the rest and inparticular with respect to the potential drop produced by grid currentat resistance I4, the manneroi operation coincides com- 45 pletely withthat according to Fig. 2.

The arrangement proposed according to the invention insures theproduction of negative impulses of suflicient size at'control grid oftube l5. An amplification of these impulses may, 50 however, beaccomplished in the manner that a feedback coil I1 is provided in thesaw-tooth generator whose one end is grounded and whose other end isconnected with the'control grid of input tube through resistance I8. 55

What I claim is: r

1. A synchronizing apparatus comprising a vacuum tube, having anode,cathode and control electrodes, means for storing electrical energyconnected in a current carrying electrode-cathode path of said tube,means for feeding back to the control electrode of said tube a portionof said stored energy during its discharge, a rectifier, resistive meansconnected to said rectifier, a source of fixed bias potentialelectrically connected to resistive means whereby the control electrodeof said tube is maintained at a predetermined bias potential, means forimpressing potentials representative of the potential fall across saidresistive means onto a control electrode of the vacuum tube, means formaintaining said tube normally conducting by impulses exceeding apredeterminable amplitude, and means for blocking said tube when saidimpulses fall below a definite value whereby said vacuum tube storesenergy in said energy storage means during periods of conduction, saidenergy being discharged during periods when the vacuum tube is blocked.

2. A synchronizing apparatus comprising a vacuum tube having anode,cathode and control electrodes, means for storing electrical energyconnected in a current carrying electrode-cathode path of said tube,means for feeding back to the control electrode of said tube a portionof said stored energy during its discharge, a rectifier, resistive meansconnected to said rectifier, a source of fixed bias potentialelectrically connected to resistive means whereby the control electrodeof said tube is maintained at a predetermined bias potential, means forimpressing potentials representative of the potential fall across saidresistive means onto a control electrode of the vacuum tube, means formaintaining said tube normally conducting by impulses exceeding apredeterminable amplitude, means for maintaining said tube currentsubstantially constant during periods of conduction, and means forblocking said tube when said impulses fall below a definite valuewhereby said vacuum tube stores energy in said energy storage meansduring periods of conduction, said energy being discharged duringperiods when the vacuum tube is blocked.

3. A sawtooth wave generator comprising means for receiving signals froma source external to the generator, means for impressing said signalsonto a first uni-directional conductor, means for developing a potentialdifierence in accordance with the current flow in said uni-directionalconductor, a thermionic vacuum tube having anode, cathode and at leastone control electrode, inductive means connected in the anode-cathodecircuit of said tube and adapted to store electro-magnetic energy fromat least a portion of the anode current of said tube, a unidirectionalconductor connected substantially in parallel with said inductive means,means for impressing the potential developed in accordance with thecurrent flow through said first uni-directional conductor onto thecontrol'electrodecathode circuit of said thermionic tube, and a sourceof fixed bias potential connected in the control electrode-cathodecircuit of said thermionic tube whereby said tube remains conductingthroughout a range of received signal amplitude values and is maintainedblocked by signals without the conducting amplitude range.

4. Apparatus in accordance with claim 3, wherein said uni-directionalconductors each comprises a diode.

5. Apparatus in accordance with claim 3, wherein there is provided inaddition resistance means connected serially with the control electrodeof said thermionic tube and the means for developing a potential inaccordance with the current flow through the first uni-directionalconductor.

6. Apparatus in accordance with claimv 3, wherein, said means fordeveloping a potential in accordancewith the current flow in the firstuni-directional conductor comprises a resistance connected serially withsaid uni-directional conductor and having the current from saidconductor passing therethrough.

ROBERT ANDRIEU.

